HUMIDITY AND CROWDING. AS THE WEATHER WARMS UP, THIS IS WHAT WE TYPICALLY SEE, PEOPLE OUT ENJOYING IT. TURNS OUT THAT IS ONE OF THREE REASONS SCIENTISTS EXPECT TO SLOW DOWN THIS SUMMER. >> PROBABLY THE MOST IMPORTANT ONE IS CROWDING. SO IN THE WINTER PEOPLE ARE INSIDE MORE. SINCE THEY ARE INSIDE MORE, THEY ARE CLOSER. >> WHEATON PEOPLE WERE OUTSIDE, HIGHER TEMPERATURES BREAK DOWN THE AIR FASTER SO IT BECOMES LESS INFECTIOUS. SAME WITH HIGHER HUMIDITY. THE VIRUS CAN'T SURVIVE AS LONG WHEN IT IS HUMID. SCIENTISTS TOOK THAT INFORMATION ABOUT THE WAY HEAT AFFECTS OUR BEHAVIOR AND THE VIRUS AND TRACKED THE SPREAD OF COVID-19 ALL-AROUND THE GLOBE. THEY FOUND THE TRANSMISSION WAS FASTEST IN AREAS THAT WERE COOL AND DRY, UP TO ABOUT 62 DEGREES. AND THEN THEY MAPPED OUT THEIR PREDICTIONS. BY RATE SUMMER, SACRAMENTO COUNTY COULD SEE JUST UNDER TWO PEOPLE INFECTED BY EVERY NEW CASE OF THE VIRUS, DOWN FROM 2.3 RIGHT NOW. THAT MEANS IT IS STILL SPREADING, JUST NOT AS FAST. THE NUMBERS ARE MUCH MORE DRAMATIC IN AREAS WITH MORE EXTREME WEATHER, LIKE PHOENIX, ARIZONA, WHERE THE RATE OF THIS SUMMER. BUT TWO POINTS TO KEEP IN MIND. IN EVERY MAP, THE VIRUS BOUNCES BACK IN THE FALL. AND WHILE THE WEATHER CAN SLOW THE VIRUS, IT WON'T STOP IT. >> IT WOULD HAVE TO BE UNBARRY BONDSLY HOT FOR COVID TO BE WIPED OUT. IT WOULD HAVE TO BE OVER 130 OR 160 DEGREES OR SOMETHING LIKE THAT TO REALLY GET RID OF IT. % BUT THE HIGHER THE TEMPERATURE, THE LESS SURVIVES. >> AND THAT MEANS THE BOTTOM LINE IS THAT WE CAN'T DEPEND ON THE WEATHER TO KEEP US SAFE FROM COVID-19. >> I THINK I KNOW THE ANSWER TO THIS QUESTION, BUT DOES THAT MEAN WE CAN LET DOWN OUR GUARD? >> NO, WE CAN'T LET DOWN OUR GUARD. IT IS REALLY IMPORTANT TO MAINTAIN THE SOCIAL DISTANCING. THAT WE CAN DO DURING THIS TIME WHEN WE DON'T HAVE A VACCINE. >> AND THE DOCTOR ESTIMATES THAT RIGHT NOW ABOUT 4% OF US HAVE BEEN INFECT THE WITH COVID-19 HERE IN CALIFORNIA. THAT MEANS THE VAST MAJORITY OF US ARE STILL SUSCEPTIBLE. OF COURSE THAT MEANS WE STILL NEED TO BE CAREFUL. >> VERY

Warmer weather may have an impact on the spread of the novel coronavirus, according to a working paper from six research institutions.With a new virus, it takes some time for scientists to understand exactly how it spreads. Many studies have looked at how weather conditions affect the transmission rate of COVID-19.“Despite multiple studies, there is currently limited agreement on the impact of weather conditions on transmission rates of COVID-19,” according to Harvard University’s “Weather Conditions and COVID-19 Transmission” projections website.Harvard is one of the institutions contributing to the paper. Researchers assembled data sets from across the world of COVID-19 infections and weather conditions, analyzing the impact of weather on virus transmission across 3,739 locations and creating projections.“Our projections suggest warmer temperature, more humidity, and moderate outdoor UV exposure may offer a modest reduction in reproductive numbers; however, upcoming changes in weather alone will NOT be enough to fully contain the transmission of COVID-19,” the website says.Sister station KCRA talked with Dr. Dean Blumberg, Chief of Pediatric Infectious Diseases at UC Davis Children's Hospital, about how the weather could have an impact on the spread of COVID-19. Blumberg, who is not affiliated with the study, said COVID-19 is following similar patterns of other viruses. He explained three weather factors impact virus transmission.Heat“The higher temperatures end up in the degradation of their (viruses) genetic material so that they become less infectious,” Blumberg said.However, summer heat doesn’t end the spread of viruses.“It would have to be unbearably hot for COVID-19 to be wiped out,” Blumberg explained. “It would have to be over 130 or 160 degrees — or something like that — to really get rid of it. But, the higher the temperature, the less it survives.”HumidityResearchers working on the study also looked at the impact high humidity played on transmission rates. They found the fastest transmission was in places with dry, cool weather with up to 62 degrees.Blumberg said viruses don’t survive long in high humidity.“With lower humidity, the virus survives longer,” he said. “It dries out our mucus membrane, our nasal passages and all. And we get cracking and other issues with our respiratory tract and that makes us more susceptible to infection.”Crowding“Probably the most important one is crowding,” Blumberg said. “In the winter, people are inside more, and since they're inside more, they're closer. We know that, for example, with COVID-19, a study from China looked at over 100 outbreaks of three or more people and all of those were related to indoor contact, none of those were related to outdoor contact."Blumberg said when people are outside, higher temperatures break down the virus on surfaces and in the air faster — so it becomes less infectious.“There's basically an infinite amount of air to dilute the virus,” Blumberg said. “Whereas indoors, there's a limited amount of air and a limited amount of air exchanges so the virus is more concentrated.”The takeawayThere are two big points to keep in mind about how weather impacts the spread of the novel coronavirus. First, all the projections show transmission rates increase in the fall and, secondly, the summer could slow the spread of the virus – but not stop it.“We can't let down our guard,” Blumberg said. “It's really important to maintain the social distancing. It's the number one thing we can do during this time when we don't have a vaccine.”

Harvard is one of the institutions contributing to the paper. Researchers assembled data sets from across the world of COVID-19 infections and weather conditions, analyzing the impact of weather on virus transmission across 3,739 locations and creating projections.

“Our projections suggest warmer temperature, more humidity, and moderate outdoor UV exposure may offer a modest reduction in reproductive numbers; however, upcoming changes in weather alone will NOT be enough to fully contain the transmission of COVID-19,” the website says.

Sister station KCRA talked with Dr. Dean Blumberg, Chief of Pediatric Infectious Diseases at UC Davis Children's Hospital, about how the weather could have an impact on the spread of COVID-19.

Blumberg, who is not affiliated with the study, said COVID-19 is following similar patterns of other viruses. He explained three weather factors impact virus transmission.

Heat

“The higher temperatures end up in the degradation of their (viruses) genetic material so that they become less infectious,” Blumberg said.

However, summer heat doesn’t end the spread of viruses.

“It would have to be unbearably hot for COVID-19 to be wiped out,” Blumberg explained. “It would have to be over 130 or 160 degrees — or something like that — to really get rid of it. But, the higher the temperature, the less it survives.”

Humidity

Researchers working on the study also looked at the impact high humidity played on transmission rates. They found the fastest transmission was in places with dry, cool weather with up to 62 degrees.

Blumberg said viruses don’t survive long in high humidity.

“With lower humidity, the virus survives longer,” he said. “It dries out our mucus membrane, our nasal passages and all. And we get cracking and other issues with our respiratory tract and that makes us more susceptible to infection.”

Crowding

“Probably the most important one is crowding,” Blumberg said. “In the winter, people are inside more, and since they're inside more, they're closer. We know that, for example, with COVID-19, a study from China looked at over 100 outbreaks of three or more people and all of those were related to indoor contact, none of those were related to outdoor contact."

Blumberg said when people are outside, higher temperatures break down the virus on surfaces and in the air faster — so it becomes less infectious.

“There's basically an infinite amount of air to dilute the virus,” Blumberg said. “Whereas indoors, there's a limited amount of air and a limited amount of air exchanges so the virus is more concentrated.”

The takeaway

There are two big points to keep in mind about how weather impacts the spread of the novel coronavirus. First, all the projections show transmission rates increase in the fall and, secondly, the summer could slow the spread of the virus – but not stop it.

“We can't let down our guard,” Blumberg said. “It's really important to maintain the social distancing. It's the number one thing we can do during this time when we don't have a vaccine.”